An EFT description is based on an expansion in a parameter encoding the scale
hierarchies which underlie the EFT description. Therefore an uncertainty arises
due to the truncation of the EFT expansion. In particular, there is the
question whether to truncate the SMEFT expansion at amplitude-squared level
strictly beyond dimension-6, or to include squared dimension-6 operators, which are
of order \(1/\Lambda ^4\)  and therefore formally suppressed at the same order as dimension-8
operators. Furthermore, double operator insertions into a single diagram are
usually neglected as they form a subset of operators at order \(1/\Lambda ^4\) 
which is not uniquely defined (for example, they can be related to a different
set of operators through the equations of motion). Such issues have been
discussed recently in
Refs. [1]}, [2]}, [3]}, [4]}.
